The development of monoclonal antibody technology has provided an enormous opportunity for science and medicine in implementing research, diagnosis and therapy. Monoclonal antibodies are e.g. used for in vitro and in vivo diagnosis as well as immunotherapy of human disease. At present, a large percentage of the biotechnology-derived drugs under development are based on monoclonal antibodies of type G. IgGs are commonly produced according to standard techniques in large quantities in cellular expression systems. The most widely used production method includes purification via chromatography, which due to its versatility and sensitivity to the compounds often is the preferred purification method in the context of biomolecules.
In the field of affinity chromatography, various patents and patent applications relate to protein A, which is an IgG-binding cell wall protein of the bacteria Staphylococcus aureus, and its use as a ligand. For example, PCT/SE83/00297 (Pharmacia Biotech AB) discloses a recombinant form of protein A, wherein a cysteine residue has been added to the protein A molecule to improve its coupling to a separation matrix for subsequent use as an affinity ligand. Further, U.S. Pat. No. 6,197,927 (assigned to Genentech Inc.) discloses Z domain variants of Staphylococcal protein A exhibiting an IgG-binding capacity equivalent to the wild type Z domain, but a significantly reduced size. However, Protein A has been shown to be protease sensitive. In addition, protein A-based affinity ligands have also been known to be unstable under acidic and basic conditions, which may result in an undesired leakage of the ligand during the purification process which will both contaminate the product and impair the quality of the purification system.
Within prior art there is a number of patent applications describing small molecule ligands having affinity for IgG:
WO 2004039765 (Amersham Biosciences AB) describes the use of phenyl urea scaffold based small molecules as chromatography affinity ligands for IgG and Fab fragments with light chain of kappa-type.
U.S. Pat. No. 6,610,630 (assigned to Ciphergen Biosystems Inc.) describes the use of 2-mercaptoimidazole and derivatives thereof attached to a solid support as pseudo bio-affinity chromatography media for selective adsorption of IgG.
U.S. Pat. No. 6,117,996 (assigned to Novo Nordisk A/S) describes the preparation of triazine based structures and their use in the purification of various proteinaceous materials.
US 20030166002 (Chang et al) describes the synthesis and selection of active compounds based on triazine structures carrying a linker suited for attachment to a resin.
EP 1500431 (Millipore UK, Ltd, UK) relates to a medium which comprises a solid support and, attached thereto, one or more affinity chromatographic ligands selected from 2-aminobenzimidazole and 2-aminomethylbenzimidazole. The affinity ligands of the invention are used for IgG purification.
In spite of the existing alternatives to Protein A for IgG binding there is still a need of novel IgG-binding ligands of a more advantageous nature. Such new ligands should avoid the above-discussed drawbacks, and preferably also involve more preferable binding properties than the hitherto suggested ligands.